Probably Territorials/Yeomanry, pre WW1. Two have the Territorial badge on their right chest, indicating willingness to serve overseas.
On the right, the difference in buttons may just mean he was improperly dressed and liable to be put on a charge if the sergeant major saw him! [Button undone or missing]
Spurs support the idea of a mounted unit, as do the riding crops. That may be the leather flap of the crop which you thought was a ribbon.
Can you scan the photo to separate one of the cap badges or shoulder titles?
A